Spray foam pros and cons

Spray foam is cool, but there are some disadvantages. The one that bothers me, that no one ever seems to mention, is that you're covering up a lot of stuff. You will no longer be able to find electrical wires or pipes or any other conduit. Larger conduit like vents or waste drains might be able to be located, but working on them is pretty much out of the question without destroying the insulation. You are basically "setting in stone" a bunch of stuff that we all know is going to need change or maintenance at some point. Comments?

Another disadvantage is that rightly or wrongly, shingle manufacturers will often void the warranty if spray foam is applied directly to the underside of the roof. Baffles might help that situation, but I see it applied without baffles all the time.

Advertisement

You almost always destroy whatever insulation you are working in so SPF bears no distinction when having to service something in that regard. Is it is easy to replace, no, but the exterior air barrier (and much of the large benefit of SPF in the fact that it is an air barrier) is persevered. Replacing it for such a small section would be cost prohibitive but if it is OC SPF, you could fill that same void with batt and be fine and largely reproduce the R-Value in the wall.

As far as the shingles, in a majority of the uses of SPF in roof assemblies, there are no baffles. You are mixing term in this case because most applications of SPF are converting the roof into a non-vented design.

Shingle manufacturers can claim all they want when it comes to ventilation but it has been shown that insulating roof decks does not change the shingle peak temperature that much or jeopardize their lifespan if we are talking about acceptable pitch values.

A darker roof is much hotter than a lighter roof that is ventilated in most cases and a majority of the shingle cooling happens via convection to outside movement across the shingles.

SPF has its place but you can typically duplicate the benefit of SPF with cheaper materials and get similar results.

As far as the shingles, in a majority of the uses of SPF in roof assemblies, there are no baffles.

Yeah I know, that's the problem.

Quote:

Originally Posted by Windows on Wash

You are mixing term in this case because most applications of SPF are converting the roof into a non-vented design.

I don't know what "mixing term" means, but the attic space is still non-vented. You're confusing the context. The baffles keep the space to the soffits open, but they don't open to the attic space. The attic space is sealed. It just allows a buffer of air an inch or 2 below the roof.

Quote:

Originally Posted by Windows on Wash

Shingle manufacturers can claim all they want when it comes to ventilation but it has been shown that insulating roof decks does not change the shingle peak temperature that much or jeopardize their lifespan if we are talking about acceptable pitch values.

Actually that is not the problem. What kills most roof assemblies is improper venting if roof is vented and the resultant moisture accumulation in the roof systems. That moisture is what degrades the deck from the bottom up and will also (depending on the underlayment type) permeate to the shingles.

This is why I prefer a synthetic underlayment in most applications because it helps eliminate the solar vapor drive.

If you have even decent pitch, a majority of the shingle cooling happens to outside.

Peak shingle temperature differences do existing between sealed/insulated roof decks and vented decks but they are not as high as you may think. Typically, a sealed roof systems will have temperature differences of 7-15 degrees on average.

Shingle color, pitch, and orientation have much more to do with shingle temps than do venting.

Quote:

Originally Posted by jeffnc

I don't know what "mixing term" means, but the attic space is still non-vented. You're confusing the context. The baffles keep the space to the soffits open, but they don't open to the attic space. The attic space is sealed. It just allows a buffer of air an inch or 2 below the roof.

Mixing terms means that you are using conflicting terms. The roof is either vented or it is sealed. There is no in between and doing half of one and half of another do not yield the best of both. More like the exact opposite.

Having a baffle and soffit with no means of exhaust air into the attic and out of the attic is a recipe for disaster.

A buffer of air in this case is more like a moisture collection zone without being able to vent.

Quote:

Originally Posted by jeffnc

Doesn't matter, do you want your roof warranty voided?

No, but spraying foam on the underside does not void the roof warranty.

Mixing terms means that you are using conflicting terms. The roof is either vented or it is sealed. There is no in between and doing half of one and half of another do not yield the best of both.
...
No, but spraying foam on the underside does not void the roof warranty.

Check the warranties.

You are still missing the point. The only one "mixing terms" here is you. I'm not saying about which is best or what technical problems might result. I understand how attics are vented. I'm saying spraying foam directly to the roof deck might void the shingle warranty, and to avoid doing so, baffles must be installed with spray foam. And I'm saying if the work is permitted and inspected, it might not pass.

"The most common speed bump I run into during [conversations with building inspectors] involves roof venting and shingles warranties. If the spray-foam insulation will void the shingle manufacturer's warranty, the inspector won't sign off on the foam. Most spray-foam manufacturers have letters (or can help you get a letter) from the shingle manufacturer to alleviate the inspector's concerns. Still, some inspectors allow spray foam under a roof only if the roof is vented. Venting a roof deck for spray foam means that baffles must cover the entire width and length of the rafter bay."

Spray Foam Concerns

On my own home I have had a problem with my 2lb spray foam. The problem is hard to determine which came first - it is like the Chicken and the Egg.

I had a 2" ABS drain line that I found cracked. This was causing a little moisture to seep out and this moisture wetted a LVL support beam not designed to get wet.

So did the beam sag and crack the pipe? I don't know.

Did the footing settle and this caused the pipe to crack and this made the beam sag? Good question.

As for spraying the bottom side of a floor which contains drain pipe I would suggest that these lengths get a few no hub fittings and then a wrap of insulation (bat style) to avoid a direct bond from the spray foam to the waste line.

Hope this says anyone the grief I went through. The insulaltion was installed by a pro. Inspected by the city.

You are still missing the point. The only one "mixing terms" here is you. I'm not saying about which is best or what technical problems might result. I understand how attics are vented. I'm saying spraying foam directly to the roof deck might void the shingle warranty, and to avoid doing so, baffles must be installed with spray foam. And I'm saying if the work is permitted and inspected, it might not pass.

"The most common speed bump I run into during [conversations with building inspectors] involves roof venting and shingles warranties. If the spray-foam insulation will void the shingle manufacturer's warranty, the inspector won't sign off on the foam. Most spray-foam manufacturers have letters (or can help you get a letter) from the shingle manufacturer to alleviate the inspector's concerns. Still, some inspectors allow spray foam under a roof only if the roof is vented. Venting a roof deck for spray foam means that baffles must cover the entire width and length of the rafter bay."

Besides taking up space that could be used for insulation value, there is no good reason to leave an air space behind sheathing in an unvented scenario.

The pdf that you linked to is referencing a vented roof design. From your pdf:

Still, some inspectors allow spray foam under a roof only if the roof is vented. Venting a roof deck for spray-foam insulation means that baffles must cover the entire width and length of the rafter bay.

In this scenario, the baffles would be installed the entire length and would carry intake air from a vented soffit all the wall to a ridge vent.

This would, by design, still be consider a vented roof design. I think we probably got a bit off track when we started talking about attic venting vs. just calling the roof vented. That was probably my fault.

This approach can be problematic if you are setting up a cathedral ceiling and you have limited rafter depth and need to get code required insulation levels in the roof assembly. There are other things you can do but that is something to chat about later.

I would still skip the baffles and make my own vent space out of rigid board.

Like this:

I agree with you that sometime inspectors are not quite up to date with what is permitted and what materials work together. As you mentioned, a letter from the shingle and foam manufacturer should clear up the gray areas.

On my own home I have had a problem with my 2lb spray foam. The problem is hard to determine which came first - it is like the Chicken and the Egg.

I had a 2" ABS drain line that I found cracked. This was causing a little moisture to seep out and this moisture wetted a LVL support beam not designed to get wet.

So did the beam sag and crack the pipe? I don't know.

Did the footing settle and this caused the pipe to crack and this made the beam sag? Good question.

As for spraying the bottom side of a floor which contains drain pipe I would suggest that these lengths get a few no hub fittings and then a wrap of insulation (bat style) to avoid a direct bond from the spray foam to the waste line.

Hope this says anyone the grief I went through. The insulaltion was installed by a pro. Inspected by the city.

cc SPF will definitely hide a bunch and I have heard stories where waste lines were broken inside walls for months without showing. That is certainly a mess than I would not like to clean up.

cc SPF will normally have enough give in it to accommodate a bit of movement but it certainly is rigid and will not give anywhere near what oc SPF will.

Is this floor above a crawlspace? cc SPF is great for vapor permeance stuff but I can't think of too many applications that you can run oc SPF and get just the same kind of functionality out of it and avoid some of those issues.

I agree with you that sometime inspectors are not quite up to date with what is permitted and what materials work together. As you mentioned, a letter from the shingle and foam manufacturer should clear up the gray areas.

I ran into this type of scenario when I was in the planning stage of an addition to my second story. I had planned on putting 4" of foam board on the outside walls, followed by cavity insulation with no vapour barrier. My GC suggested that it would be cheaper and faster to install the barrier for the inspection, then rip it off before drywalling, than try to explain to the inspector in the area why it wasn't necessary

After reading this I am confused. I thought baffles were required when spray foaming the underside of a roof. After reading this post I have come to two conclusions. Before I insulate I am going to run the whole job past you guys. Next, I will probably just go with the fiberglass batts because I know what to expect with the fiberglass. I have found that baffles are needed in cold northern climates even with fiberglass batts. I insulated a cathedral ceiling that was Not vented and had mold after one winter. I made my own baffles from ridge board and put new insulation up. I guess every situation is a little different. I am still hoping oil will go to 15 dollars a barrel and we can just go back to not using insulation

Another disadvantage is that rightly or wrongly, shingle manufacturers will often void the warranty if spray foam is applied directly to the underside of the roof. Baffles might help that situation, but I see it applied without baffles all the time.

Most of those warrantees aren't worth the paper they are printed on anyway, they will LOOK for ways to get out of it by citing things like not enough vents, not properly installed, you name it.

cc SPF will definitely hide a bunch and I have heard stories where waste lines were broken inside walls for months without showing. That is certainly a mess than I would not like to clean up.

The Friday before the spray foam was to be done I discovered the plumber had failed to glue the elbows on a waste line for a sump pump. 6am the following Monday and he was there rectifying his mistake. Otherwise, yeah, it might have been a real hassle to repair, let alone discover the problem.

Yes, it's certainly easier to rip open a wall and remove fiberglass insulation should something in there need repair. But there's the trade-off between the benefits of foam insulation in the meantime. Should you actively plan for very unlikely repairs and lose the insulating benefits? Or just be aware the costs to repair will be somewhat higher if there's ever a very unlikely failure? We opted for the latter.